Hillary Clinton’s longtime confidante, Huma Abedin, hasn’t been seen on the campaign trail since FBI Director James Comey sent a letter to Congress Friday notifying them of new emails that may be related to Clinton’s private email server.

The source of those emails is a laptop belonging to Abedin’s estranged husband, former congressman Anthony Weiner, that is part of a separate investigation into sexually explicit electronic messages he allegedly sent to a minor. Abedin had turned over other devices as part of the FBI probe into Clinton's server and has said she doesn’t know how the emails turned up on Weiner’s laptop.

On Monday morning, as Clinton boarded her campaign plane in Westchester, N.Y., en route to events at Kent State University and Cincinnati, reporters traveling with the Democratic presidential nominee did not spot Abedin, who was last seen at Clinton's side on Friday, when news broke of Comey's letter. The campaign hasn’t responded to a request for more information about plans for her to return to the trail.

Abedin has worked for Clinton since she was a 19-year-old White House intern in the 1990s, and Clinton has likened her to a second daughter. Abedin was expected to take on a senior role in a Clinton White House, should the Democratic nominee defeat Donald Trump, after having served as a vice chair on the campaign and a top aide to Clinton at the State Department.

The FBI has obtained a warrant to review the emails linked to Abedin, an official who is not authorized to comment publicly told USA TODAY Sunday. It’s possible, said the official, that many of them are duplicates of those already reviewed by the FBI earlier this year.